130 



THE AMERICAN MONTHLY 



[July, 



The contents of this are transformed 

 into an indefinite number of resting- 

 spores, the contents of which become 

 converted into a number of sexual, 

 copulating swarmspores (microzoo- 

 spores) . 



Propagation also by cell-division 

 and formation of asexual swarm-cells 

 (macrozoospores) . 



53. Genus Botrydium Wallroth. 



Vegetative plant, a large, green, 

 single cell, spherical or balloon-shape 

 above the ground, tapering downward 

 to a coloi'less, branching subterranean 

 root (rhizoid). 



Propagation by cell-division, forma- 

 tion of uniciliate zoospores, and cop- 

 ulating biciliate zoospores. 



By division of the aerial portion an 

 outgrowth is divided oft' which grows 

 to the size of the mother-cell, develops 

 a rhizoid, and finally becomes a sepa- 

 rate plant. 



The contents of the cell (zoospo- 

 rangium) may divide into numerous 

 macrozoospores,each with one cilium, 

 which escape, lose their cilia, acquire 

 a membraneous covering and germi- 

 nate {Protococcus botryoides) on 

 moist earth. 



The contents of the green cell may 

 also give rise to a number of spores, 

 at first green, changing to red (^Pro- 

 tococcus coccojjia^ palustris^ botry- 

 oides), which in water produce 

 biciliate zoospores (microzoospores). 

 These copulate and form spherical 

 zygospores (also named isospores). 

 These inay germinate immediately, or 

 pass into a resting condition. 



[The processes of propagation are 

 variously modified by the conditions 

 of gro"wth, especially by the amount 

 of water present. The phenomena 

 that have been observed are confusing 

 and difficult to understand, but they 

 affbrd an excellent example of adap- 

 tation to changing conditions.] 



P'amily V. Vaucheriace^. 



Thallus filamentous, rather robust, 

 unicellular, aerial and aquatic, large. 

 The entire plant is a single, long tube, 

 usually branched. The protoplasm 

 forms a thin layer on the walls, in 



which are chlorophyll-grains, and oil- 

 drops. Usually there are hair-roots at 

 the lower end. 



Sexual propagation by oogonia and 

 antheridia. Oogonia spherical, lat- 

 eral on the frond, stalked or sessile. 

 Antheridia colorless, polymorphic, 

 lateral on the frond, within which 

 form numerous spermatozoids, ^vhich 

 escape throvigh an opening, enter the 

 oogonia, and fertilize the oosphore. 

 The resulting oospore is inclosed by 

 several coats. After a period of rest 

 it germinates and grows to a new 

 plant. 



Asexual proj^agation by gonidia, 

 which in many species are motile, in 

 others not, and germinate in a short 

 time. 



54. Genus, Vaucheria De Can- 

 dolle. 



Oogonia and antheridia produced in 

 indefinite number near together on 

 the same individual, sessile or on pedi- 

 cels. Antheridia either sac-shape or 

 elongate and curved cells ; sperma- 

 tozoids elongate, with two cilia usu- 

 ally of unequal length. 



Zoospores formed in terminal cells, 

 which are divided oft' from the fila- 

 ments by a septum after an accumu- 

 lation of dark protoplasm occurs at 

 the ends. A single spherical or oval 

 zoospore is formed in each cell, 

 which escapes by an opening. The 

 motile zoospores are covered with 

 cilia, and after a short time they come 

 to rest and germinate. The motion- 

 less ones likewise germinate soon after 

 their escape. 



[The life-history of Vaucheria has 

 been presented in an interesting man- 

 ner on pages 2 to 6 of the current 

 volume. The species are numer- 

 ous.] 



[ To be continued. ] 



Improved Microscope Objectives. 



The following notice of the recent 

 work of Mr. Gundlach has been sent 

 to us by a correspondent, which we 

 publish for the information of our 

 readers. The new lenses are worthy 

 of a trial : — 



